Chairman Graham Wheeler said the group has secured a further three years of government and community funding to complete its investigation.
Tutsan now costs some landowners up to $400 a hectare a year to control.
An economic assessment found there is $2.3 million a year in direct and indirect costs, with a capital cost to New Zealand of up to $32m because of the reduction in land values.
Over the past three years, TAG has contracted Landcare Research to study tutsan in NZ and in its native ranges in Europe and the United Kingdom and to look for insects and diseases attacking it.
Two insects – a moth (Lathronympha strigana) and a beetle (Chrysolina abchasica) – have been found attacking tutsan in Georgia. Both appear to be quite damaging and relatively host-specific to tutsan.
They will be brought to NZ for intensive research and testing over the next three years.
If they are found to be successful in attacking NZ tutsan Environmental Protection Authority (EPA) approval will be sought for the release of one or both insects.
Researchers will also continue their search for a new rust that could be effective on North Island tutsan.
Wheeler says biocontrol offers a cost-effective, environmentally-friendly and permanent solution to weed control.
TAG has now raised $1.2m from contributors including the Ministry for Primary Industries’ Sustainable Farming Fund, Horizons and other regional councils, Landcare Research, Ruapehu District Council, Department of Conservation, Treescape/Kiwirail, territorial authorities, Maori-owned enterprises, forestry, community groups and more than 150 farmers.
TAG was formed in 2007 by a group of farmers with Horizons Regional Council, DOC and Landcare Research in response to concern at the increasing spread of this invasive pasture weed.
Tutsan exists all over NZ but is a significant problem in parts of the central North Island where it forms extensive patches that threaten agricultural, forestry and conservation land.
Unpalatable to stock, hard to kill and shade-tolerant, tutsan is particularly prevalent in areas where the land has been disturbed by the likes of forestry – much like gorse and broom.
It is easily spread by birds, mowers, machinery and soil and water movement.
Common seed sources include roadsides, conservation and wasteland, old gardens and forestry.
Serious tutsan infestations throughout NZ in the 1950s almost disappeared thanks to the self-introduced rust (Melampsora hypericorum).
But while the rust appears to still be effective in the South Island, it has become largely ineffective in the North Island.
